1. Field of the Invention
This invention relates to air conditioning systems and specifically to a method and apparatus for controlling the discharge pressure of the compressors in a unitary fan, multi-split system.
2. Description of the Prior Art
Control of compressor discharge pressure by fan cooling for air conditioning systems to protect against low discharge levels is well known in the art. If adequate pressure is not maintained at low ambient temperatures, the evaporator temperature may drop below freezing on cold days and cause condensation moisture to freeze on the evaporator coil. The resulting layer of ice tends to insulate the coil from the refrigeration mode and causes a further reduction in system capacity.
Control of compressor discharge pressure by unitary fan cooling has not heretofore been used in a multi-split air conditioning system. The fan control is used on a multi-split system to prevent freeze up of a fan coil when it is the only one running. On a multi-split unit, when all fan coils are operating the suction pressure stays up and the fan coils will not freeze. However, when just one fan coil is running, the suction pressure and temperature will drop and the coil may freeze. By properly controlling the outdoor fan the discharge pressure may be kept up, keeping the suction pressure up and preventing the coil from freezing. Difficulties arise, however, when a single fan is used with multiple coils. This is because one coil may require its fan to be on while the other does not.